Composite color-plus-clear coatings are widely utilized in the coatings art. They are particularly desirable where exceptional gloss, depth of color, distinctness of image, or special metallic effects are required. The automotive industry has made extensive use of color-plus-clear composite coatings for automotive body panels.
As used herein, the term "composite color-plus-clear" relates to composite coating systems requiring the application of a first coating, typically a colored basecoat coating, followed by the application of a second coating, generally a clearcoat, over the noncured or "wet" first coating. The applied first and second coatings are then cured. Thus, such systems are often described as "wet on wet" or "two coat/one bake". Drying processes which fall short of complete cure may be used between the application of the coatings.
Clearcoats used in color-plus-clear systems must have an extremely high degree of clarity in order to achieve the desired visual effects. High gloss coatings also require a low degree of visual aberrations at the surface in order to achieve the desired visual effect such as high distinctness of image (DOI). As a result, clearcoats of color-plus-clear systems are especially susceptible to the phenomenon known as environmental etch, i.e., spots or marks on or in the clear finish that often cannot be rubbed out.
Although many compositions have been proposed for use as the clearcoat of a color-plus-clear composite coating, prior art clearcoat coatings often suffer from disadvantages such as coatability problems, compatibility problems with the colored basecoat, solubility problems, and/or insufficient resistance to environmental etch.
Clearcoat coating compositions exhibiting many advantages over prior art compositions, especially with respect to environmental etch, were disclosed in U.S. Pat. Nos. 5,474,811 and 5,356,669. The disclosed clear coating compositions comprise a first component comprising a polymer backbone having appended thereto at least one carbamate functional group, and a second component comprising a compound having a plurality of functional groups that are reactive with said carbamate groups.
Surface imperfections and/or defects can occur during the multistep application process typically used to apply composite coatings. Such surface imperfections and/or defects are sometimes not repairable until after the curing of the composite coatings. In some instances, the repair process occurs subsequent to the addition of other components to a coated article. The additional components may have melting or deformation temperatures which are lower than the cure temperature of the original composite coating.
Ideally, it would be desirable to repair surface imperfections and/or defects with the original composite coating or component coatings thereof, in order to obtain uniform appearance and performance properties over the whole of the coated article. In particular, it would desirable to provide a repair coating which provides the same performance and appearance properties of the original composite coating or a component coating thereof.
However, the cure schedule for traditional composite coatings typically requires temperatures greater than the melt or deformation temperature of some article components added subsequent to the original composite coating application process.
Thus, there is a need for a curable coating composition suitable for use in low bake repair of color-plus-clear composite coatings or coating components thereof.
More particularly, there is a need for a curable coating composition which can be used in low bake repair of color-plus clear composite coatings or components thereof, which provides desirable performance and appearance properties and cures at a temperature less than that of the cure temperature required for the original color-plus-clear composite coating.
It would be particularly advantageous to provide a curable coating composition for use in low bake repair of color-plus clear composite coatings which provides the advantages of carbamate functional resin containing coatings and cures at a temperature of 200.degree. F. or less, especially 190.degree. F. or less.
Desirable performance properties in a low bake repair curable coating composition are good solvent resistance, hardness and environmental etch resistance.
The low bake repair curable coating composition should also cure at curing conditions which make repair commercially feasible and advantageous, i.e., 5 to 15" at 200.degree. F. or less.
Advantageous appearance properties are a colorless appearance, high DOI, and a glossy appearance over a wide range of basecoat and clearcoat film thickness.